• 한국세라믹학회지
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• 제43권10호
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• pp.595-600
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• 2006

The preparation of $\beta$-SiAlON powder by SHS in the system of $Si-Al-SiO_2-NH_4F(\beta-Si_3N_4)$ was investigated in this study. In the preparation of SiAlON powder, the effect of gas pressure, compositions such as Si, $NH_4F$, \beta-Si_3N_4$ and additive in mixture on the reactivity were investigated. At 50 atm of the initial inert gas pressure in reactor, the optimum composition for the preparation of pure $\beta$-SiAlON was $3Si+Al+2SiO_2+NH_4F$. The $\beta$-SiAlON powder synthesized in this condition was a single phase $\beta$-SiAlON with a rod like morphology.

• 한국응용곤충학회지
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• 제8권
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• pp.19-23
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• 1969

질소원, 탄소원을 달리하여 배양한 Fusarium oxysporium f. cucumerinum에 Grand 유제를 농도별로 처리했을 때 균사의 발육신장에 미치는 영향에 대하여 비교 검토한 실험결과를 보면 다음과 같다. (1) Fusarium oxysporium f. cucumerinum은 질소원이 $(MH_4)_2HPO_4,\; NH_4NO_3$인 배지에서 탄소원은 Fructose 배지에서 균사의 발육신장이 양호하였다. (2) 각종 질소원과 탄소원에서 배양한 균을 Grand유각 1,000배액을 처리하면 다같이 균사의 발육이 완전히 조지되었으며 5,000배액에서는 영양원의 종류에 따라 차이가 있어 $NH_4NO_3$배지, Lactose배지, Fructose 배지에서 배양한 균만 생육이 조지되고 기타 영양원에서 배양한 균은 균사의 신장은 되었으나 무처리에 비해 어느정도 억제되는것 같다. 10,000배액에서는 모든 종류의 영양원에서 배양한 균이 균사의 신장이 일어났는데 무처리에 비해 생육이 촉진되는 것도 있고 $NH_4NO_3$ 배지, Fructose배지에서 배양한 균은 오히려 억제되는 것도 있었다. (3) 이상 연구결과로 보아 Grand유제는 농도와 오이 만할병균이 영양상태에 따라 살균력에 영향을 주는것으로 사려된다.

• Journal of Oral Medicine and Pain
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• 제21권1호
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• pp.115-122
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• 1996

This study was performed to compare the anticarious effect of the different fluoride adsorbed(Naf, $NH_4F, Na_2PO_3F, SnF_2, TiF_4$) on synthetic hydroxyapatite and enamel. The amount of fluoride adsorbed in synthetic hydroxyapatite under various concentrations and pH of these fluoride solutions was measured by specific electrode. Enamel samples treated with 5 kinds of 1,000ppm fluoride solutions for 10 minutes were evaluated for fluoride uptake and enamel soubility. The results were as follows. 1. The adsorption of fluoride on synthetic hydroxyapatite increased gradually by the concentration of the fluoride solution, In 1,000ppm fluoride solution, the adsorption of fluoride on synthetic hydroxyapatite treated with NH4F and NaF solutions at pH 4.0 was relatively higher than that of other fluoride solutions. In NH4F and NaF solutions, the adsorption of fluoride on powdered enamel was higher at pH 4.0 solution than at pH 7.0 solution. 2. Fluoride uptake from NH4F solution was relatively high. But that from $Na_2PO_3F$ solution was lower than those from other fluoride solutions. 3. Fluoride solutions were significantly effective on enhancing acid resistance. $NH_4F$ solution was relatively more effective than others on enhancing acid resistance. 4. $SnF_2 and TiF_4$ solutions had the same effect on fluoride adsorption, fluoride uptake, and enamel solubility.

• 한국재료학회지
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• 제15권6호
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• pp.408-412
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• 2005

[ $Ba_{1.5}Sr_{0.5}SiO_4:Eu$ ] phosphor particles with high photoluminescence intensity under long wavelength ultraviolet were prepared by spray pyrolysis. We investigated the effect of $NH_4F$ flux added into starting solution on the morphology and photoluminescence intensity of $Ba_{1.5}Sr_{0.5}SiO_4:Eu$ phosphor prepared by spray pyrolysis. $Ba_{1.5}Sr_{0.5}SiO_4:Eu$ phosphor particles prepared from starting solution containing $NH_4F$ flux had the maximum photoluminescence intensity at the post-treatment temperature of $1200^{\circ}C$ and the maximum photoluminescence intensity of $Ba_{1.5}Sr_{0.5}SiO_4:Eu$ phosphor particles prepared from the starting solution containing $NH_4F$ flux was $137\%$ of that of the phosphor particles prepared from the starting solution without flux material. $Ba_{1.5}Sr_{0.5}SiO_4:Eu$ phosphor particles prepared from starting solution containing $NH_4F$ flux had larger size and more aggregated morphology than those prepared from starting solution without flux material. The photoluminescence intensity of $Ba_{1.5}Sr_{0.5}SiO_4:Eu$ phosphor particles prepared from starting solution containing $NH_4F$ flux above $3wt.\%$ had high photoluminescence intensities. The addition amount of $NH_4F$ flux showing the maximum photoluminescence intensity was $12wt.\%$. The optimum amount of $NH_4F$ flux was $5wt.\%$ when we considered the morphological and photoluminescence characteristics of $Ba_{1.5}Sr_{0.5}SiO_4:Eu$ ohosphor particles prepared by spray pyrolysis.

• 센서학회지
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• 제8권5호
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• pp.414-420
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• 1999

희생층을 제거하는 기술은 표면 마이크로머시닝 공정의 핵심기술중 하나이다. 그러나 희생층을 제거하는데 널리 쓰이는 BHF 용액을 포함한 HF 수용액은 희생층 제거시 금속층으로 쓰이는 알루미늄도 같이 식각하는 것으로 알려져 있다. 기존의 문헌에서 $NH_4F$:HF:glycerine=4:1:2의 비를 갖는 혼합 용액이 알루미늄과 PSG 간의 식각 선택비가 최적조건으로 제시되었지만 이 희생층 식각액 또한 상당한 알루미능 식각률을 가지고 있다. 본 논문에서는 HF, $NH_4F$, glycerine의 농도를 광범위하게 변화시켜 희생층 제거에 필요한 최적 혼합비를 개발하였으며 그 결과 $NH_4F$:HF:glycerine=2:1:4의 혼합비에서 약 7,700정도의 PSG와 Al의 식각 선택비를 가져 기존의 최적 식각 선택비보다 차수가 약 6배정도 향상된 희생층 식각액을 얻을 수 있었다. 이 조건에서 PSG의 식각률은 희생층 제거시 충분히 빠른 값인 약 $2.1\;{\mu}m/min$을 나타내었다. 이러한 개발된 희생층 식각액은 표면 마이크로머시닝 공정에서 알루미늄 금속 공정의 추가를 용이하게 한다.

• 대한화학회지
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• 제39권7호
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• pp.552-558
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• 1995

배위자인 이소부틸, 노르말 부틸 및 메틸티오아세트아미드옥심과 출발 물질인 단핵 및 다핵 착물과의 반응에서 $X_2[M_{O4}O_12{R'C(NH_2)NO}_2](X=n-Bu_4N^+$, $R'=(CH_3)_2CH$, $CH_3CH_2CH_2$, $CH_3SCH_2$; $X=(CH_3)_2CHC(=NH_2)NH_2^+$, $R'=(CH_3)_2CH$; $X=CH_3CH_2CH_2C(=NH_2)NH_2^+$, $R'=CH_3_CH_2CH_2$; $X=CH_3SCH_2C(=NH_2)NH_2^+$, $R'=CH_3SCH_2)$을 합성하였다. 합성한 착물은 원소분석, 적외선 및 핵자기공명에 의해 구조를 규명하였다. 얻은 착물중 ${(CH_3)_2CHC(NH_2)_2}_2[M_{O4}O_{12}{(CH_3)_2CHC(NH_2)NO}_2]$은 X-선 단결정 회절에서 결정구조를 밝혔고, 얻은 데이타는 Monoclinic, $P2_{1/c}$, $a=10.168(3){\AA}$, $b=11.768(1){\AA}$, $c=13.557(1){\AA}$, ${\beta}=102.08(1)^{\circ}$, $V=1586.2(5){\AA}^3$, Z = 2이었고, 회절강도 2951개($F_0>3s(F_0)$)에 대한 최종 신뢰도 인자는 0.026이었다. 이 착물의 구조는 평면상의 환형$[Mo_4({\mu}-O)_4]$과 두 개의 ${\mu}_4$-아미드옥시메이트로 구성되어 있다.

• Nuclear Engineering and Technology
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• 제51권3호
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• pp.792-799
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• 2019

The present study aims to investigate the fluorination of thorium oxide ($ThO_2$) by ammonium hydrogen difluoride ($NH_4HF_2$). Fluorination was performed at room temperature by mixing $ThO_2$ and $NH_4HF_2$ at different molar ratios, which was then left to react for 20 days. Next, the mixtures were analyzed using X-ray diffraction (XRD) at the intervals of 5, 10, 15, and 20 days, followed by the heating of the mixtures at $450-750^{\circ}C$ with argon gas flow. The characterization of $ThF_4$ was established using X-ray diffraction (XRD) and scanning electron microscopy-dispersion X-ray spectroscopy (SEM-EDX). In this study, ammonium thorium fluoride was synthesized through the fluorination of $ThO_2$ at room temperature. The optimum molar ratio in synthesizing ammonium thorium fluoride was 1.0:5.5 ($ThO_2:NH_4HF_2$) with 5 days reaction time. In addition, the heating of ammonium thorium fluoride at $450^{\circ}C$ was sufficient to produce $ThF_4$. Overall, this study proved that $NH_4HF_2$ is one of the fluorination agents that is capable of synthesizing $ThF_4$.

• 한국표면공학회지
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• 제55권1호
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• pp.24-31
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• 2022

This study investigated the effect of pre-treatment on the PEO film formation of AZ91 Mg alloy. The pre-treatment was conducted for 10 min at room temperature in 0.5 M oxalic acid (C₂H₂O₄) solution containing various ammonium fluoride (NH₄F) concentrations. The pre-treated AZ91 Mg specimens were anodized at 100 mA/cm² of 300 Hz AC for 2 min in 0.1 M NaOH + 0.4 M Na₂SiO₃ solution. When AZ91 Mg alloy was pretreated in 0.5 M oxalic acid with NH₄F concentration less than 0.3 M, continuous dissolution of the AZ91 Mg alloy occurred together with the formation of black smuts and arc initiation time for PEO film formation was very late. It was noticed that corrosion rate of the AZ91 Mg alloy became faster if small amount of NH₄F concentration, 0.1 M, is added. The fast corrosion is attributable to fast formation of porous fluoride together with porous oxides in the reaction products. On the other hand, when AZ91 Mg alloy was pretreated in 0.5 M oxalic acid with sufficient NH₄F more than 0.3 M, a thin and dense protective film was formed on the AZ91 Mg alloy surface which resulted in faster initiation of arcs and formation of PEO film.

• Corrosion Science and Technology
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• 제17권3호
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• pp.138-145
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• 2018

The aim of this work is the attainment of the $TiO_2-nanotube$ photocatalytic-growth condition using anodization, whereby the $NH_4F-H_2O$ weight ratio is appropriately controlled. We fabricated the $TiO_2$ nanotubes using a two-step anodization (first step is 1 hr; second step is 30 hr) under the ambient pressure and the room temperature at 60 V in ethylene-glycol solutions to investigate the effects of the $NH_4F$(0.1,0.3,0.5wt%) and $H_2O$(1-3wt%) on the $TiO_2-nanotube$ geometry and the photocatalytic efficiency. Further, the decomposition efficiency of the methylene blue on the $TiO_2$ nanotubes by the UN radiation depended on the geometrical change of the nanotube geometry, indicating the proportionality of the decomposition efficiency to the surface area that was affected by the $NH_4F$ and $H_2O$ concentrations. As the $NH_4F$ weight was increased, the surface area initially decreased but slightly increased later, and the length consistently increased. As the $H_2O$ weight was increased, the surface area and length initially increased, but later decreased with the 3 wt% $H_2O$.

• 한국세라믹학회지
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• 제39권2호
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• pp.204-209
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• 2002

본 연구에서는 AUC 공정에서 발생되는 액체폐기물에 미량 함유되어 있는 우라늄을 회수/재사용하기 위해 액상에서 침전법을 이용하여 용해도가 작은 우라늄화합물을 얻었으며, 이 화합물에 대한 chemical analysis, thermal analysis, x-ray diffraction analysis 및 FT-IR 분석을 통해 물성 특성을 해석하였다. 연구결과, 화학분석 및 FT-IR 분석으로부터 우라늄화합물은 $UO_4{\cdot}2NH_4F$ 형태를 가지고 있음을 알 수 있었으며, 평균 2∼3${\mu}m$ 입자 크기를 갖는 hexagonal 형태를 나타내었다. 열 분해시 분해 온도에 따라 중간물질로 $UO_4F,\;UO_4,\;UO_3,\;U_3O_8$ 등으로 변환되었으며, 상온에서 800$^{\circ}C$까지의 공기분위기에서 일정한 가열속도로 열분해시킬 경우, $UO_4{\cdot}2NH_4F{\rightarrow}UO_4F{\rightarrow}UO_4{\rightarrow}UO_3{\rightarrow}U_3O_8$의 반응 메커니즘을 나타내었다.